A number of lines belonging to the v3 fundamental vibration-rotation band of hydrogen cyanide (HCN) have been identified in atmospheric infrared absorption spectra obtained on high-altitude balloon flights at 32¿N in 1976 and at 30¿S in 1977. Quantitative analysis of these spectral features has resulted in the first determination of atmospheric HCN concentrations in the southern hemisphere, as well as an independent estimate of stratospheric HCN abundance in the northern hemisphere. Within the uncertainties of our own and previous measurements, our northern-hemisphere result is consistent with those of other investigators, and southern-hemisphere HCN concentrations appear to be similar to those in the northern hemisphere.